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53 Cards in this Set

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  • Back
what are the 3 major roles of the thyroid hormone?
stimulate basal metabolic rate
protein, carb, & lipid metabolism
normal growth & development
thyroid hormone is synthesized from?
iodine and tyrosine
what are the 3 proteins that can bind thyroid hormone?
TBG, TBPA, albumin
how is T3 synthesized?
20-25% biosynthesized
the rest is made from converted T4
which is more potent, T3 or T4?
T3
what percentage of T3 is free? T4?
FT3 = 0.2%
FT4 = 0.02%
what controls the release of thyroid hormones?
TSH
thyroid stimulating hormone
what controls the release of TSH?
TRH
thryoid releasing hormone
what is the negative feedback system that controls TSH & TRH
intracellular T4 and T3
what has a negative effect on thyroid production?
intrathyroidal iodide
how are the concentrations of TSH and FT4 related?
they are logarithmic (a 50% reduction in FT4 leads to a 50 fold incr of TSH)
what is hypothyroidism?
a decr in T4 and T3
what is thyrotoxicosis?
a incr in T4 and T3
what is primary hypothyroidism?
related to the thyroid gland itself
deficiency or excess of iodide
what is secondary hypothyroidism?
related to the pituitary
reduced TSH (hypopituitarism)
what is tertiary hypothyroidism?
reduced TRH
hypothalamic dysfunction
thyrotoxicosis: overproduction caused by
graves
carcinomas
TSH secreting adenomas (benign tumor)
thyrotoxicosis: leading thyroid hormone destruction caused by
sub acute thyroiditis
radiation
what is subacute thyroiditis?
inflammation of the thyroid gland that usually follows an upper respiratory infection and then subsides
drugs that can cause thyrotoxicosis
excess thyroid replacement
iodinated radiocontrast agents
what are the s/s of thyrotoxicosis?
cardiac arrhythmias
nervousness
sweating
goiter
what are the s/s of hypothyroidism
sensitivity to cold
depression
weight gain
constipation
what are the 4 tests for diagnosing and monitoring thyroid function?
concentration of hormones
intrinsic thyroid gland function
integrity of axis
antibodies to thyroid gland
for the concentration of hormones test, which hormones are looked at?
free T4
total serum T4
serum T3 resin uptake
free T4 index
total serum T3
which thyroid hormone concentration is the best measure of thyrometabolic status?
free T4
why is free T4 difficult to measure?
because it is in such a low concentration
concentration test using FT4 is used when
there are alterations in T4 binding globulins
nonthyroidal illness confounds interpretation
FT4 reference range
0.8 to 1.5 ng/dL
what is the diagnosis if you have lowered FT4 and incr TSH
primary hypothyroidism
what is the diagnosis if you have incr FT4 and decr TSH?
non pituitary hyperthyroidism (primary)
if you have low TSH and low FT4, you should treat with?
T3
what can cause abnormal lab results in a FT4 concentration test?
severe T4 binding alterations
total serum T4 concentration is used as?
a standard screening test (widely available & quick turnaround time)
reference range for total serum T4
4 to 12 ug/dL
incr in total T4 may indicate
hyperthyroidism
incr thyroid binding proteins
non-thyroid illness
decr in total T4 may indicate
hypothyroidism
decr in thyroid binding proteins
non thyroid illness (euthyroid sick syndrome)
how is the total serum T4 test conducted?
radio immunoassay method
the specimen is serum
what can cause abnormal incr in serum T4 lab results
incr TT4 in minor illness (esp elderly)
transient decr in TSH
incr TT4 in psychiatric patients
what can cause an abnormal decr in total serum T4 lab results
decr thyroid binding proteins (neoplastic disorders, DM, burns, liver disease, renal disease, trauma, prolonged infection)
drugs that can incr TBP
heroin
estrogen
methadone
drugs that can decr TBP
salicyates
glucocortoids (high dose)
furosemide (high dose)
drugs that can incr TT4 and FT4
iopdate
iodides
propanolol
drugs that can decr TT4 and FT4
lithium carbonate
sulponamides
antacids
what data does serum T3 resin uptake test give?
indirect estimate of number of binding sites
can verify clinical significance of measured TT4 & TT3
what does the serum T3 resin uptake test differentiate between?
low T3 secondary to nontyroidal illness from ture hypothyroidism
reference range for serum T3 resin uptake
25-34%
serum T3 resin uptake results for hypothyroidism
low TT3 and FT3
normal TBP
low T*3 uptake (33%)
serum T3 resin uptake results for hyperthyroidism
low TT3 and FT3
low TBP (low # binding sites)
incr T*3 uptake (66%)
what can cause abnormal lab results in the serum T3 resin uptake test?
all disease staes & drugs that alter TBG
radioactive substances taken by patients
what is the serum T3 resin uptake test used to calculate
free thyroxine index (FTI)
what is the rationale behind the free thyroxine index?
adjusts for effects of TBP alterations
FTI referance range
1.0-4.0units
calculation for FTI
FTI = TT4(mg/dL) X T3 resin uptake (%)